The present invention relates to measuring the presence or concentration of an analyte in a sample, particularly by spectrophotometry. In particular, the present invention relates to a device and method for stabilizing a cuvette while the cuvette is in the measurement station of an analyzer.
Spectrophotometer and photometer measurement systems have historically been designed so that the cuvette is motionless during the read or measurement process. See, e.g., U.S. Pat. No. 5,774,209. To increase system throughput, specialized spectrophotometers and photometers have been designed to take readings while the cuvette is moving. A related class of moving cuvette measurement systems stops the motion of the cuvette and immediately takes a reading. The shorter delays after cuvette motion stops, and the shorter read integration times result in faster system cycle time and generally translates into more tests processed per hour, i.e., higher throughput. Throughput of a system is an important measure that determines the value of an analyzer system to users and is of significant importance in marketing diagnostic analyzers. Known diagnostic analyzers having cuvettes include those described in U.S. Pat. Nos. 4,595,562; 5,774,209; 5,849,247; 4,517,160; 5,380,666 and Re. 30,391.
Some known analyzers, such as the Vitros® Fusion 5,1 analyzer developed by Ortho-Clinical Diagnostics, Inc. or Konelab™ 60 sold by Thermo Electron Corporation use a multi-cell cuvette as shown in FIG. 1, containing rows of separate test cells, such as a row of 6 or 12 separate test cells. The entire cuvette consisting of, e.g., 6 cells must be read very quickly, on the order of about 1.5 seconds to keep up throughput. The design is to read each of the cells after it has stopped. As described in copending patent application Ser. No. 10/784,505, filed Feb. 23, 2004, entitled “Determining An Analyte By Multiple Measurements Through A Cuvette”, which is incorporated herein by reference in its entirety, the preferred measurement read process is to take multiple measurement readings (preferably 3) at each of the 6 cells in a cuvette during each read cycle. By taking three measurement reads per cell, the cuvette needs to start/stop 18 times for each row of 6 cells. The larger number of reads require a shorter integration time for each measurement read (20 ms instead of the standard 100 ms).
Tests with the cuvette being completely static showed that a reduction in measurement read integration time to 20 ms does not substantially degrade photometer precision. However, in some cases, such as large number of measurement reads in short period of time, there was substantial degradation in photometer precision. In fact, actual test data with the cuvette stopped immediately before the measurement read demonstrated that the shorter integration times were often 10 times to 100 times more imprecise. If there was any movement, it was believed in the art that the chopping system for the photometer would cancel out errors due to movement of the cuvette during the measurement read process. However, this was not the case.
The problem of cuvette imprecision was particularly noticeable in systems in which the cuvette is supported at one end by the cuvette handling system, such as by a hook or other devices, such that the cuvette is cantilevered. In those systems, test data showed a pattern where the last three cells in the cuvette (the ones furthest away from a conveyor system that captures the cuvette by cantilevering the cuvette at one end) were often significantly more imprecise. In addition, the data also showed that the first of the three measurement reads within a cell was often more precise than the other two.
None of the known art described above, adequately addresses resolving the problems described above, in particular, of improving precision of measurements in multi-cell cuvettes in the measurement station of an analyzer
For the foregoing reasons, there is a need for a device and method to improve the precision of measurement reads in a multi-cell cuvette.